A typical printing apparatus is based on a subtractive color model and uses subtractive colorants such as, for example, C (cyan), M (magenta), Y (yellow) and K (black) inks. By overprinting images for each of the colorants, an image with a range of different colors can be printed. Colorants such as these mostly reflect light with a range of wavelengths in one part of the electromagnetic spectrum and mostly absorb light with a range of wavelengths in a different part of the electromagnetic spectrum. Such colorants partly reflect and partly absorb light at each wavelength. The relative proportion of incident light that is reflected and absorbed varies with wavelength. For example, a cyan colorant reflects incident light with wavelength in the green and blue parts of the electromagnetic spectrum and absorbs other, red-looking wavelengths of electromagnetic radiation. Subtractive colorants such as these reduce the amount of light which is reflected compared with the amount of light reflected by a bare substrate without the colorant arranged on it. There is thus a limit to the brightness of colors printed in this manner.